1. Field of the Invention
The present invention relates to a silicon-controller rectifier, particularly to an asymmetric bidirectional silicon-controlled rectifier, which has a small area, adjustable trigger voltage and high electrostatic-discharge protection capability. The proposed silicon-controller rectifier can apply to an ESD protection element for I/O ports with signal of positive and negative voltage.
2. Description of the Related Art
With the increasing request of transistors count, CMOS(Complementary Metal Oxide Semiconductor) have been developed to a submicron or even deep-submicron scale. The thin gate oxide layer of the submicron or deep-submicron technology is easy to damage under higher voltage level. In common conditions, the electrostatic discharge (ESD) voltage may cause several thousands voltage, which will easily damage integrated circuits (IC) product.
The silicon-controlled rectifier with a low turn-on resistance, low capacitance, low power consumption and high-power current conduction capability is an effective ESD protection device for IC product.
Currently, the bidirectional silicon-controlled rectifier (SCR) has become the mainstream of the ESD protection circuits for I/O ports with signal of positive and negative voltage. Moreover, many publications and researches are also dedicated to the bidirectional silicon-controlled rectifier. For example, U.S. Pat. No. 6,258,634, No. 6,365,924 and No. 7,034,363, all disclosed symmetric bidirectional silicon-controlled rectifiers, which have lower ESD robustness because they are all directly fabricated on a silicon substrate. Due to symmetric structures of symmetric SCR, large layout consumption will be cost issue. Therefore, the SCR disclosed above only apply to a generic IC process. U.S. Pat. No. 6,960,792 disclosed a symmetric bidirectional SCR with annular structure, which needs a larger layout area under the fabricated process, which cannot provide an effective ESD protection because the trigger-on speed is deeply influenced by the structure thereof. U.S. Pat. No. 5,072,273 disclosed a low trigger voltage silicon-controlled rectifier, which is unidirectional application for positive voltage signal only. U.S. Pat. No. 7,145,187 disclosed a special structure of silicon-controlled rectifier, which is hard to mass production.
Accordingly, the present invention proposes a novel asymmetric bidirectional silicon-controlled rectifier to solve the problem mentioned above.